1. Field of the Invention
The present invention relates to a filtering assembly for a feedthrough, preferably for implantable medical devices, wherein said feedthrough comprises at least one operating conductive pin and a ground conductive pin and a respective feedthrough assembly.
2. Description of the Related Art
Feedthrough assemblies are generally well-known in the art for connecting electrical signals through the housing or case of an electronic instrument, for example of an active implantable medical device, such as a cardiac pacemaker, an implantable hearing device, a defibrillator, a neurostimulator, a drug pump or the like.
A known feedthrough assembly comprising a multitude of electrically conductive pins is disposed within a respective one of a multitude of openings in an insulator structure for feedthrough passage from the exterior to the interior of the electronic instrument. The end of each cylindrically formed pin of the multitude of electrically conductive pins protruding to the exterior of the electronic device is referred to as the first end of each pin and the opposite end of the each pin is referred to as the second end. The second end of the pin is electrically connected to an interior element of the electronic instrument transferring or receiving the electrical signals. The known feedthrough assembly further comprises an insulating element (in the following: header) having a supportive surface with a flange and/or a recess on the outer perimeter thereof. This supportive surface serves as a leakproof attachment of the feedthrough assembly to the housing.
Today it is often requested with regard to active implantable medical devices to decouple and/or shield undesirable electromagnetic interference signals (EMI signals) from the device wherein electromagnetic interference signals consist of a number of modulated carrier frequencies, for example the carrier frequency of a cellular phone.
In order to filter (decouple and/or shield) these undesirable electromagnetic interference signals it is well-known in the art that EMI feedthrough capacitors can be attached to the flanges of human implantable seals. These devices are generally designed with one or more monolithic ceramic feedthrough capacitors which are typically made of a barium titanate dielectric into which alternating active and ground electrode plates are embedded.
In U.S. Pat. No. 6,822,248 B2 an EMI filtered connector is disclosed which provides a multitude of conductive terminal pins, a grounded conductive connector housing through which the terminal pins pass in a non-conductive relation, and an array of feedthrough filter capacitors each having a distinct first set of electrode plates (refers to a set of electrode plates which are distinctly separate and associated with a particular capacitor of the feedthrough filter capacitor array), a non-distinct second set of electrode plates (refers to those plates which are common to two or more of the distinct capacitors in the array of feedthrough filter capacitors) and first passage way through which a respective terminal pin extends in conductive relation with the first set of electrode plates. Further, at least one ground lead conductively coupled to the conductive connector housing and extending into a second passage way through the array of feedthrough filter capacitors in conductive relation with the second set of electrode plates and a grounding ring conductively coupled to the ground lead and to the connector housing are provided.
Document U.S. Pat. No. 6,987,660 B2 describes feedthrough capacitors which are typically formed of a dielectric material having disposed therein in an alternating fashion ground electroplates and active electroplates. A passage way is provided through the capacitor which is lined with a metallization layer typically applied either by a thick film process or by selective electroplating. Additionally, metallization is applied about the periphery of the capacitor in a similar manner as the interior metallization. The exterior metallization provides the electrical contact to the ground electrode plate set. For conductively coupling the terminal pin and the first set of electrodes and for mechanically coupling the terminal pin to the feedthrough capacitor the feedthrough terminal assembly described in this document comprises a terminal pin which at least partially extends through the aperture. A conductive insert is disposed within the aperture. In one embodiment, the insert further comprises a resiliently flexible conductive contact spring which provides the electrical contact between the inside diameter of the feedthrough hole of the ceramic capacitor and the lead wire of a terminal pin.
The above mentioned state of the art feedthrough assemblies for EMI filtering have the disadvantage, that on the one hand they are expensive in manufacturing and on the other hand it is impossible to get reliable results in leakage testing because of their complicated structure. Additionally, the state of the art feedthrough assemblies can not easily be minimized.
In U.S. Pat. No. 6,459,935 B1 a filtered feedthrough assembly is disclosed comprising a header having a supportive surface and a discoidal capacitive device with an upper and a lower side, wherein the lower side is connected or bonded to the supportive surface of the header. The discoidal capacitive device comprises a first set of electrode plates arranged to be suitable for parallel connections with the multiple electrically conductive terminal pins, a second set of electrode plates arranged to be suitable for series connections with the multiple electrically conductive terminal pins and a second set of openings defined through said discoidal capacitive device for the passage of the terminal pins, wherein electrically conductive patterns are disposed on said upper side of said discoidal capacitor and an electrical component is connected to said electrically conductive patterns. The discoidal capacitor is bonded to the supportive surface of the header with a conductive polyamide. This feedthrough assembly can be manufactured more easily and less expensively than the feedthrough assemblies above mentioned and allows for the integration of additional electronic components into the assembly. However, the direct connection or bonding of the discoidal capacitive device to the supportive surface of the header may cause difficulties in the manufacturing procedure and result in less reliability during its operation because the header and the discoidal capacitive device have different thermal expansion coefficient.
Therefore it is desirable to provide a multi-leaded feedthrough assembly and a filtering assembly therefore capable of reliably filtering EMI at the point of entry of the signals into the implantable medical device and which can be manufactured easily and inexpensively, tested with reliable results and allows for integration of further electrical components.